1. Field of the Invention
The present invention generally relates to a zoom lens system, and more particularly to a zoom lens system capable of maintaining a given magnification during a change in the photographing distance of an object on which the lens system is focused. The capability of this form of zoom lens system is especially useful in a motion picture or television camera when shooting an object which is gradually approaching or receding.
2. Description of the Prior Art
When an object to be photographed moves along the optical axis, constant magnification photography may be achieved by adjusting the focus of the lens system in response to the change in the object distance and also by adjusting the focal length to correct for the change in magnification due to the change in the object distance. In the prior art, it is known to connect the zooming means to the focusing means in a predetermined manner so that a zooming operation, to off-set the change in magnification, may also automatically accompany the focusing operation to focus the system on the moving object. However, the manner in which the zooming means is connected to the focusing means must be predetermined with respect to a specific magnification. The particular structural arrangement, accordingly, has to be altered if a constant magnification photography at another magnification is desired.
U.S. Pat. No. 4,083,057 discloses a constant magnification photography lens system, wherein changes in the position of the taking lens are accompanied by changes in the zoom focus system. Swiss Pat. No. 481,389 is also cited of interest.
The prior art is still seeking a constant magnification zoom lens system that is relatively inexpensive.